Fly-by-wire

ABSTRACT

Three separately generated electrical control signals are applied to respective electromechanical transducers in a power actuator control system. Each electromechanical transducer generates a mechanical output motion related to the applied control signal and independent of the remaining transducers. A mechanical linkage arrangement coupled to the outputs of each of the three electromechanical transducers combines the motions into a single mechanical movement. This single mechanical movement positions the control element for a servo-pump supplying a power actuator.

United States Patent Redmond, Jr. July 25, 1972 s41 FLY-BY-WIRE3,426,650 2/1969 Jenney ..9l/363 A x 3,505,929 4/1970 Coppola et al.....9l/4l1 R X [72] wiu'am kedmm" Dallas 2,898,889 8/1959 Foster ..244/85[73] Assignee: LTV Electrosystems, lnc., Greenville, Tex. 3,027,378 1962K y 6 /73 X 3,422,767 1 196 M Al l 5 22 Filed: July 20, 1970 9 vay 9[21] Appl. No.: 56,551 Primary Examiner-Milton Buchler AssistantExaminer-F. K. Yee Attorney-Richards, Harris & Hubbard and James D.Will- [52] 0.8. Cl. ..244/77 R, 91/411 R, 244/78, born 244/85, 318/564[51] Int. Cl. ..B64c 13/50 57 B TR [58] Field of Search ..244/ R, 75 A,76 R, 76 A,

244/76 B, 76 C 77 R. 77 v, 78' 83 R 83 E 85; Three separately generatedelectr cal control signals are up- 91/363 A, 363 R, 411 A 411 B 411 R I505407; plied to respective electromechanical transducers In a power74/479; 235/61 A 61 C, 417/222 426; actuator control system. Eachelectromechanical transducer 318563465 generates a mechanical outputmotion related to the applied control signal and independent of theremaining transducers. A mechanical linkage arrangement coupled to theoutputs of [56] References Cned each of the three electromechanicaltransducers combines the UNITED S ES PATENTS motions into a singlemechanical movement. This single mechanical movement positions thecontrol element for a 3,554,084 l/l97l Rasmussen et al. ..9l/4li R Xservo pump supplying a power actuaton 3,469,162 9/1969 Goshn ..3l8/5643,401,600 9/ 1968 Wood ..91/4ll R X 5 Claims, 4Drawing Figures a2 66 so74 o 2o 78 a0 a 22 as e iir'e I a4 SUPPLY /0\ 40 54 62 7o 76 25 J 26 3o42 45 72 5' a 7 a 46 56 36 I2 34 32 3e 92 44 SERVO SERVO a PUMP PUMP I424 SO-f 50 52 COMPARATOR CHANNEL MONITOR SELECTOR PATENTEDJULZS 1912SHEET 8 [IF 2 INVENTOR: WILLIAM G. REDMOND, JR.

ATTORNEYS FLY-BY-WIRE This invention relates to redundant electricalcontrol, and more particularly to redundant electrical control employingdisplacement summing techniques.

It was early realized that as aircraft increase in size and speed thatconventional cable and mechanical linkage control mechanisms areinadequate and there is a need for electrical flight control systems.There has, however, been some reluctance to accept the electrical flightcontrol system because it is thought that mechanical systems are morereliable. To improve the reliability of electrical control, a system ofredundant parallel channels has been implemented.

I-Ieretofore, approaches for providing redundancy have typicallyresulted in double or triple control chains or channels in which afailure in one channel hopefully would permit the other channels tocarry on the necessary command functions. Such a system, depending uponthe particular failure suffered, generally experienced at leastdegradation of control when the failed channel must be dragged by theoperating channel or channels. Because most electrical failures are notjust loss of electrical power or other passive failures but are oftenhardover or other grossly discrepant commands, three or more redundantchannels are frequently employed. In the usual redundant control, thecomplete system from the signal generating source to the control surfaceis repeated. As the number of redundant channels increases,synchronization of the control motion at the control surface becomes aproblem.

In the typical push rod and cable controlled mechanical systems,dual-tandem hydromechanical power servos are used with each sectionthereof provided with a separate hydraulic supply. The signal orintelligence paths to the power servo is mechanical and single, exceptat the dual servo for controlling the hydraulic fluid to the dualhydromechanical power servo. In such systems, synchronization isfeasible and easily accomplished. In the dual hydromechanical powerservo systems, the failure of one of the hydraulic systems is passiveand not fighting the remaining operating system. These last two featuresof mechanical system have, heretofore, not been found in the redundantelectrical control signal.

An object of the present invention is to provide a redundant electricalcontrol system terminating at a single power actuator. Another object ofthis invention is to provide a redundant cal motion equal to the sum ofthe individual movements. This single mechanical motion is connected toa power actuator which responds thereto and has an output controllingthe movement of the aircraft control surface.

A more complete understanding of the invention and its advantages willbe apparent from the specification and claims and from the accompanyingdrawings illustrative of the invention.

Referring to the drawings:

FIG. 1 is a schematic of the redundant control system includingdisplacement summed electromechanical transducers for controlling adual-tandem power actuator connected to a control surface;

FIG. 2 is a cross section of an electromechanical transducer for thesystem of FIG. 1;

FIG. 3 is a sectional view of a motor driven variable displacementservo-pump for controlling hydraulic fluid to the power actuator of thesystem of FIG. 1; and

FIG. 4 is a schematic of a three channel comparator system.

Referring to FIG. 1, there is shown a fly-by-wire redundant controlsystem wherein the electrical portion is made triply redundant to give alow probability of all channels failing during a single operation. Thethree electrical channels are totally independent; the output of eachbeing summed in the form of position or displacement" summationtechniques of mechanical movements of electromechanical transducers l0,l2, and 14. Each of the electromechanical transducers is energized by aseparately generated electrical signal. The electrical signals may begenerated by a pilot control stick transducer that converts a mechanicalmotion into electrical signals. In addition to the pilot generatedsignals, the electrical signals to the transducers may be received fromautopilot sensors, a stability augmentation system, or from othersystems, such as a navigation control.

Although the system to be described has electromechanical transducers ineach control channel, other electrically responsive transducers may beused. For example, electrohydraulic transducers responsive to anelectrical signal and generating a electrical control system withoutchannel synchronization. A

further object of this invention is to provide a redundant electricalcontrol system wherein a failure of one channel does not light theremaining operating systems. Still another object of this invention isto provide a redundant electrical control signal having a lowprobability of all channels failing during a control operation.

In accordance with the present invention, redundant control channels areemployed to improve the system reliability. The several electricalchannels terminate at a single power actuator that positions the controlsurface of an aircraft. The several channels of the system aredisplacement summed that is, the output of each channel is combined by amechanical linkage arrangement to generate a single motion related tothe sum of all the channels. Displacement summing has the advantage thatthe remaining active channels do not have to drag a failed channel. Whenthe several redundant channels are combined to produce the total desiredmovement of the aircraft control surface, a failure of one of thesechannels results in some loss of stroke of the power actuator, with theattendant loss in the range of movement of the control surface, butcontrol is maintained. Further, with displacement summing, over-strokecapability in each of the three channels can be built into each actuatorto provide full stroke upon the loss of a single channel.

In accordance with a more specific embodiment of the invention, anaircraft control system for positioning a control surface in response toelectrical control signals includes at least three transducers eachhaving an output motion related to an electrical control signal appliedthereto. Each of the output motions of the individual transducers aredisplacement summed such that the combination results in a singlemechanimechanical motion through hydraulic action may be used.

Each of the electromechanical transducers 10, 12 and 14 operatesindependent of each other. For example, a signal for energizing thetransducers 10 is supplied from an amplifier 16 connected to a powersupply 18 and receiving an input signal from a summing junction 20. Thesumming junction 20 differentially combines the electrical controlsignal from the source, as explained, with a feedback signal from aposition transducer 22. Similarly, the transducer 12 is energized by asignal from an amplifier 24 coupled to a power supply 26 and receivingan input signal from a summing junction 28. The summing junctiondifferentially combines the control signal for the transducer 12 with afeedback signal from a position transducer 30. The third channel,containing the electromechanical transducer 14, is similar to theprevious two. The transducer 14 is energized by a signal from anamplifier 32 connected to a power supply 34 and receiving an inputsignal from a summing junction 36. The summing junction 36differentially combines a control signal for the transducer 14 with afeedback signal from a position transducer 38.

Each of the transducers 10, 112, and 14 thus produces a unique outputmotion for the electrical control signal applied thereto. The separatemechanical motions are summed by mechanical summing linkages 40 and 42.Summing link 40 combines the output motion of the transducer 10 with theoutput motion of the transducer 12. The summing link 42 combines themovement of the summing link 40 with the output motion of the transducer14. With the arrangement illustrated, each of the transducers has a gainfactor (a fraction of the total motion) equal to one-third of the totaloutput motion produced by the links 40 and 42, as evidenced by themechanical motion of a connecting rod 44.

The combined movement of the transducers l0, l2, and 14 is imparted tothe connecting rod 44 coupled to lever arms 46 and 48 of variabledisplacement servo-pumps 50 and 52,

respectively. As an alternative, instead of servo-pumps, the connectingrod 44 may be coupled to a power servo using a flow-controlled servovalve. An over limit stop 54 is provided for the connecting rod 44 tolimit the travel thereof to the maximum allowable displacement of thelever arms 46 and 48. This over limit stop thus absorbs the excessmovement at the output of each of the transducers 10, 12, and 14 whenprovided with over-stroke capability. The lever arms 46 and 48 areinterconnected by a synchronizing arm 56 having a synchronizingadjustment nut 58. In the system shown, this is the only synchronizationrequired. This adjustment is made when the system is initially put intooperation.

The servo-pumps 50 and 52 are part of separate hydraulic sourcesconnected to a dual-tandem power actuator 60. Conduits 62 and 64 connectthe servo-pump 50 to the first stage of the actuator 60 on oppositesides of a piston 66. A pressure relief valve 68 is connected betweenthe conduits 62 and 64 in accordance with standard procedures. Conduits70 and 72 similarly interconnect the servo-pump 52 to the second stageof the power actuator 60 on opposite sides of a piston 74. Again, apressure relief '76 interconnects between the conduits 70 and 72.

Pistons 66 and 74 of the power actuator 60 are interconnected on apiston rod 78 that has an external coupling to a link 80. Link 80 isintended to represent the mechanical linkage between the power actuator60 and one of the control surfaces 82 of an aircraft. Also connected tothe piston rod 78 is a follow-up (feedback) rod 84 for repositioning thelever arms 46 and 48 in response to movement of the control surface 82.

As illustrated, each electrical control channel culminates in amechanical link displacement with the three displacements of thetransducers 10, 12 and 14 added to give a single mechanical input to thedual hydromechanical system including the actuator 60. Each channel gaincan have as much percentage tolerance as would a single, non-redundantcontrol system; the resultant percentage tolerance from the three summedchannels will be no greater than the percentage tolerance of eachchannel. Also, the phase angle of each of the three channels does notneed to be more precise than for a single non-redundant system, therebyalleviating the synchronization problem.

Referring to FIG. 2, there is shown in cross section theelectromechanical transducer for the actuator system of FIG. 1. Theother transducers of the system are similarly constructed. Asillustrated, the rotary-to-linear motion transducer has a permanentmagnet stator 120 in a housing 122. Pilot generated signals are appliedto the transducer through a connector 124 to a brush ring 125 and thento an armature 126 in the form of a DC motor, an AC motor may also beused or a brushless DC motor. The armature 126 rotates by theinteraction between its electrical field and the magnetic field of thestator 120. It is mounted to rotate in the housing 122 by means ofbearings 128 and 130. A ball nut 131 is fixed to the armature 126 andengages a lead screw 132 that extends through the housing 122 as part ofthe output shaft 133. Linear motion results from the operation of thelead screw 132 and the ball nut 131; this motion is imparted to theshaft 133 which in turn is connected to the mechanical summing link 40.To produce this linear motion, the lead screw 132 is restrained fromrotating by means of a dowel pin 134.

Also, included as part of the transducer is a linear voltagedifferential transformer 136 threaded into the housing 122 and engagingthe lead screw 132 for generating two identical position feedbacksignals. These feedback signals are transmitted through the connector124 to the summing junction 20 and to a comparator monitor, as will beexplained.

An output motion from the transducer 10, as evidenced by movement of thelead screw 132 is transmitted to the at- I tachment point of themechanical link 40 through a neutralizer 138. A neutralizer is amechanical means by which a majority vote" of the respective actuatoroutputs can be transmitted to the connecting rod 44. Similarneutralizers are provided for each of the remaining channels. Thetransducer 12 includes a neutralizer 140 and the transducer 14 includesa neutralizer 142.

Thus, a malfunctioning channel may be automatically neutralized by meansof the respective neutralizer. The neutralizers primary function is toremove a transducer in a hardover" failure condition. A hardover failureis where a channel operates in opposition to the remaining channels. Inthe hardover" failure condition, it is desirable to automaticallyde-energize and neutralize a malfunctioning channel.

Referring to FIG. 3, there is shown in section a simplified diagram ofthe variable displacement servo-pump 50 with the lever arm 46 coupled toa rotatable swash plate 144. The servo-pump 52 of FIG. 1 may be similarto that illustrated in FIG. 3 with the lever arm 48 interconnected tothe lever arm 46 through the synchronizing arm 56.

Conduits 62 and 64 are connected to the pump housing 146 throughinlet/outlet connectors 148 and 150. These connectors have openings to apiston block 152 that contains a plurality of pistons, such as pistons154 and 156, arranged in a circular pattern. The piston block 152 iscoupled to the drive shaft of a motor 158, FIG. 1, through a pump shaft160.

The operation of the pump is conventional with the pump capacity andfluid direction established by an angular position of the swash plate144. By coupling the swash plate 144 directly to the connecting rod 44through the mixing link 45 as also connected to the follow-up rod 84,there is eliminated the need for the usual hydraulic actuator heretoforeused to position the swash plate of a servo-controlled variabledisplacement pump. Further, with the electromechanical transducerscoupled directly to the servo-pump swash plate, the hydraulics of thesystem are separated from the electrical fly-by-wire portion.

With the system illustrated, the failure combination situation isimproved by not jeopardizing the hydraulic system by tying theelectrical-mechanical transducers directly thereto. Any one or two ofthe electromechanical transducers may fail and at the same time eitherof the hydraulic systems can fail and control of the surface 82 will bemaintained.

To sense the failure of any of the electromechanical transducers 10, 12,or 14, each is provided with a second position transducer connected to acomparator monitor 86. Thus, the transducer 10 includes a positiontransducer 88 generating a feedback signal to the comparator monitor 86.Similarly, the transducer 12 includes a position transducer generating afeedback signal to the monitor, and the transducer 14 includes aposition transducer 92 generating a feedback signal to the comparatormonitor. The comparator monitor 86 determines when one channel disagreeswith the other two by more than a predetermined limit and generates asignal to a channel failure indicator 94. The comparator monitor 86 alsoautomatically de-energizes and neutralizes (centers) the disagreeingchannel. This indicator may be located at the pilots position forinformation or possible override of a faulty monitor cutting off a goodchannel.

Referring to FIG. 4, there is shown one embodiment of a comparatormonitor for a three channel redundant system. Position signals from thetransducers 88 and 90 are applied to input terminals of differentialamplifiers 96 and 98. Similarly, position signals from the transducers90 and 92 are applied to the inputs of differential amplifiers and 102.Position signals from the transducers 88 and 92 are also applied toinputs of differential amplifiers 104 and 106.

Each of the differential amplifiers has a saturated output stage suchthat the output signal is either at a cut-off voltage level or asaturated voltage level. The input section of each of the amplifiersincludes circuitry such that if the upper terminal is at a highervoltage level than the lower terminal, the output stage will be cut offand if the upper terminal is at the lower voltage level, the outputstage will be operating at saturation. The input voltage differentialrequired to switch the output stage may be set by an amplifier adjacent.Such amplifiers are conventional in the art.

The output voltage from each of these amplifiers is applied to inputs ofan arrangement of NAND-gates 108 through 113 in the configuration asillustrated. Output terminals of the NANDS 108 and 109 are applied toNOR-gate 114. Output terminals of the NANDS lland 111 are similarlyconnected to a NOR gate-116 and outputs of the NANDS 112 and 113 areconnected to a NOR-gate 118.

With all three channels operating properly, the output of each of theNORS 114, 116, and 118 will be at a logic ZERO level. Should any one ofthe three channels differ by a preset amount, (a differential amplifiersetting) from the other two, one of the NOR gates will switch to a logicONE level. As connected, when the transducer 10 fails the output of theNOR 114 will switch to a logic ONE level. If the transducer 12 fails,the output of the NOR 116 will switch to a logic ONE level, and if thetransducer 14 fails, the output of the NOR 118 will change to the logicONE level. it should be understood that the comparator logic of FIG. 4is only one example of a comparator monitor 86 that may be used with thesystem of FIG. 1.

With the system as illustrated and described, each electrical channel isprovided with displacement capability sufficient to satisfactorilycontrol an aircraft (perhaps with somewhat less than full surface throwbut possibly with full-stroke capability) should one or more of theother channels be neutralized. The gain of each channel will be variedin accordance with the number of channels operating, that is, with threeoperating channels, each will contribute about one-third the totalmovement of the connecting rod 44. With more than one channel operating(normal condition) it is possible that the mechanical stop 54, whichlimits the stroke command to the servo-pumps 50 and 52, will be reached,and the electrical actuators will be neutralized. This, however, is asatisfactory condition. The system described has the further advantagein that all channels are active when in the normal operating mode.

While only preferred embodiments of the invention, together withmodifications thereof, have been described in detail herein and shown inthe accompanying drawings, it will be evident that various furthermodifications are possible without departure from the scope of theinvention.

What is claimed is:

1. A system for positioning a control element in response to electricalcontrol signals, comprising:

at least three electro-mechanical transducers each having an outputmotion related to an electrical signal applied thereto,

mechanical summing linkage coupled to the output of each of saidtransducers such that each transducer contributes to a single mechanicalmotion by an amount inversely proportional to a number of saidtransducers,

a position transducer at each of said electro-mechanical transducersgenerating a first feedback signal and a second feedback signal,

means for summing said first feedback signal with one of the electricalcontrol signals to selectively control the respective electromechanicaltransducer,

comparing means monitoring each of the second feedback signals andgenerating an indication when one differs from any combination of atleast two of the other second feedback signals, and

actuator means responsive to the single mechanical motion of saidmechanical summing linkage and having an output controlling the movementof the control elements.

2. A system as set forth in claim 1 including neutralizing means at eachof said transducers to effectively disconnect the associated transducerfrom said mechanical summing linkage.

3. A control system as set forth in claim 2 wherein said actuator meansincludes a duo-tandem hydraulic actuator responsive to the singlemechanical motion of said summing linkage and having an outputcontrolling the movement of the control element.

20 4. An aircraft control system for positioning a control surface inres onse to electrical control signals comlprisjng:

at least ee electro-mechamcal transducers avrng an output motion relatedto a separate electrical signal applied thereto,

mechanical summing linkage coupled to the output of each of saidtransducers such that each transducer contributes to a single mechanicalmotion by an amount inversely proportional to the number of saidtransducers,

a position transducer at each of said electro-mechanica] transducersgenerating a first feedback signal and a second feedback signal,

means for summing said first feedback signal with one of the electricalcontrol signals to selectively control the respective electromechanicaltransducer,

comparing means monitoring each of the second feedback signals andgenerating an indication when one differs from any combination of atleast two of the other second feedback signals,

a duo-tandem hydraulic actuator having an output controlling themovement of the control surface, each section of said actuator suppliedoperating fluid from a separate source, and

pump means for each of said supply sources for controlling the fluidtherefrom to the respective actuator stage, said pump means having apositionable swash plate coupled to the single mechanical motion of saiddisplacement summing means.

5. An aircraft control system as set forth in claim 4 includingneutralizing means at each electromechanical transducer to effectivelydisconnect the respective transducer from said mechanical summinglinkage.

1. A system for positioning a control element in response to electrical control signals, comprising: at least three electro-mechanical transducers each having an output motion related to an electrical signal applied thereto, mechanical summing linkage coupled to the output of each of said transducers such that each transducer contributes to a single mechanical motion by an amount inversely proportional to a number of said transducers, a position transducer at each of said electro-mechanical transducers generating a first feedback signal and a second feedback signal, means for summing said first feedback signal with one of the electrical control signals to selectively control the respective electromechanical transducer, comparing means monitoring each of the second feedback signals and generating an indication when one differs from any combination of at least two of the other second feedback signals, and actuator means responsive to the single mechanical motion of said mechanical summing linkage and having an output controlling the movement of the control elements.
 2. A system as set forth in claim 1 including neutralizing means at each of said transducers to effectively disconnect the associated transducer from said mechanical summing linkage.
 3. A control system as set forth in claim 2 wherein said actuator means includes a duo-tandem hydraulic actuator responsive to the single mechanical motion of said summing linkage and having an output controlling the movement of the control element.
 4. An aircraft control system for positioning a control surface in response to electrical control signals comprising: at least three electro-mechanical transducers having an output motion related to a separate electrical signal applied thereto, mechanical summing linkage coupled to the output of each of said transducers such that each transducer contributes to a single mechanical motion by an amount inversely proportional to the number of said transducers, a position transducer at each of said electro-mechanical transducers generating a first feedback signal and a second feedback signal, means for summing said first feedback signal with one of the electrical control signals to selectively control the respective electromechanical transducer, comparing means monitoring each of the second feedback signals and generating an indication when one differs from any combination of at least two of the other second feedback signals, a duo-tandem hydraulic actuator having an output controlling the movement of the control surface, each section of said actuator supplied operating fluid from a separate source, and pump means for each of said supply sources for controlling the fluid therefrom to the respective actuator stage, said pump means having a positionable swash plate coupled to the single mechanical motion of said displacement summing means.
 5. An aircraft control system as set forth in claim 4 including neutralizing means at each electromechanical transducer to effectively disconnect the respective transducer from said mechanical summing linkage. 